Electromechanical assemblies based on suspended nanotubes and other molecular-scale electrically conductive and mechanically flexible wires and their use as motors, generators, pumps, fans, compressors, propulsion systems, transmitters, receivers, heat engines, heat pumps, magnetic field sensors, magnetic field generators, inertial energy storage, and acoustic energy conversion are described in U.S. Pat. No. 7,196,450 to Pinkerton et al. (which patent is incorporated herein by reference).
Thermally driven excitations of multi-wall carbon nanotubes (MWNTs), clamped at one end only, were investigated by Treacy et al. (Nature 1996, 381, 678). Electrically driven mechanical vibrations of multiwalled nanotubes was observed by Poncharal et al. (Science, 1999, 283, 1513). Babic et al. (Nano Letters 2003, 3(11), 1577) later described thermally driven mechanical vibrations of suspended doubly clamped single-wall carbon nanotubes (SWNTs) in thermal equilibrium at room temperature, and calculated the Young's modulus of CVD-grown SWNTs from the measured rms vibration amplitude. In U.S. Patent Application Publication No. 2009/0020399, Kim et al provided an electromechanical switch that included an elastic conductive layer (that included at least one layer of graphene) that moved by the application of an electric field.
Microelectromechanical systems (MEMS) and nanoelectromechanical switch systems (NEMSS) that are structured around nanotubes have been developed. Such systems are described, for example, in U.S. Pat. No. 7,148,579 and U.S. Pat. No. 7,256,063 to Pinkerton et al (which patents are hereby incorporated herein by reference). These NEMSS can employed as transistors, amplifiers, variable resistors, adjustable diodes, inverters, memory cells, and energy conversion devices.
In some cases, a carbon nanotube is anchored at one end to an electrical contact. The opposite end of this nanotube is unattached and free to move. By inflicting an electric field on the nanotube when it carries an electric charge, the position and oscillation of the free-moving end of the nanotube can be controlled (e.g., by either repelling or attracting the nanotube). Manipulating the location of the free-moving end of such a nanotube can be utilized to realize many electrical components. For example, a transistor may be realized by configuring the nanotube such that when an appropriate electric field is applied to the nanotube (e.g., a minimum base or gate threshold voltage), the free moving end of the nanotube couples to an electrical contact (e.g., an emitter or drain terminal). Thus, if the anchored end of the nanotube is also coupled to an electrical contact (e.g., collector or source terminal) current may flow through the nanotube when the threshold voltage is met.
Appropriate magnetic fields may also be applied to a partially anchored nanotube. In doing so, the free-moving end of the nanotube may be held in contact, as a result of the magnetic field, with an electrical contact (e.g., emitter or drain contact) when current is flowing through the nanotube. The basic structure of a NEM transistor can also be configured, utilized, or adjusted to provide the functionality of amplifiers, adjustable diodes, inverters, memory cells, and automatic switches.
A nanotube-based NEM transistor of the present invention can have a very low minimum turn-ON voltage. Thus, miniscule voltage signals such as, for example, Johnson noise signals, can be sensed and manipulated. A minimum turn-ON voltage can be selected by adjusting, for example, the charge, length, width, temperature, and elevation of a nanotube.
Nanotube-based NEM transistors can also function as sensors. More particularly, if a strong magnetic field is not applied to a NEM transistor, then the free-moving end of the nanotube will couple to an emitter terminal and a tunneling current will flow at a rate dependent upon the intensity of the electric field created by the base terminal in combination with the charge density of the nanotube. As the intensity or polarity of the electric field created by the base terminal changes, the number of coupling events per unit of time that occur between the nanotube and the emitter contact will change.